The present invention relates to a method for faciltating the dialog between a subscriber to a system of pay-television (pay-TV) and a decoder of the signals received. It relates also to this decoder.
In a pay-TV system or similar systems, the subscriber selects the programs of interest and he pays for receiving these programs which are transmitted in a scrambled or encoded mode in order not to be recognizable to non subscribers or to subscribers who have not chosen nor paid for a particular program. The signals may be transmitted by cable, antenna or satellite. The sophisticated systems of pay-TV further allow for the possibility of "pay-per-view" which permits a subscriber to purchase programs either immediately before the beginning of the emission or during the emission itself and this by means of an unidirectional transmission system. In this case, it becomes necessary to memorize a certain credit at the location of the user, credit which is available for permitting the user to purchase and receive an emission pay-per-view that the user desires. If the memorized credit is sufficient, the amount is debited from the credit and the signal received from the transmitting station is unscrambled or decoded for permitting a comfortable reception thereof.
The document WO 81/02499 relates to a method and a system for scrambling the transmission of video information, more particularly for pay-TV. Parts of the video signal, e.g. parts or segments of the lines or of the frames are transmitted in a sequence different from the natural one. The manner of rearranging the sequence of the segments of lines for the transmission may be controlled by a code generator which changes the sequence at each frame or even as a function of another appropriate time base. The code which can be enciphered changes at random and it may be transmitted completely or partially with the scrambled video signal.
The U.S. Pat. No. 4,484,217 relates to a method and a system for billing at a distance a program of pay-TV. The credit available is memorized at the location of the subscriber and a cost signal is transmitted by the transmitter. Pay-per-view is made possible by the fact that there is foreseen an impulse purchase. A unique code may accompany the transmitted signal for identification purpose. If the decoder of the subscriber recognizes the program as a program purchased by impulses, the program cost is displayed. In order to visualize the program, the subscriber enters an adequate demand in the decoder and the latter compares automatically the cost of the program with the credit available. If the cost does not exceed the credit, the program is unscrambled and the cost is deducted from the credit. However, such, a system does not foreseeably display in the form of teletext transmitted by the video signal information relating to the forecasted emissions in their chronological order nor display information in the form of instructions for the manipulation to be executed by the user on the decoder, in order to facilitate the dialog between the latter and the user and to avoid manipulation errors.